French mathematician and engineer Gustave-Gaspard de Coriolis was mentored by Augustin-Louis Cauchy, and gave the terms work and kinetic energy their modern scientific meanings. He conducted important research into ergonomics, friction, hydraulics, and machine performance, but his most important contribution to science was his description of the Coriolis force (sometimes called the Coriolis effect). Caused by the Earth's rotation, the Coriolis force makes moving objects, oceans, and atmospheric systems rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Contrary to popular misconception, the Coriolis force is infinitesimal in something as small as a draining bathtub, and it has no practical influence on which way such a small whirlpool swirls. Coriolis also wrote an advanced mathematical theory explaining billiards.